The saturation values that depend on parameters such as the wettability and the interfacial tension must be known at any point in order to determine the distribution of the oil and gas volumes in a reservoir or an aquifer. To that effect, the wettability of rocks with respect to the water and the oil that can be contained therein is determined. To that effect, rock drainage operations have to be carried out, i.e. a displacement of the fluids intended to decrease the water saturation, followed by imbibition operations, this term referring to a displacement of the fluids allowing the water saturation (Sw) of the rock to be increased. The capillary pressure at a point of a porous material containing two fluids such as water and oil in the continuous phase is defined, as it is well-known, as the difference Pc at equilibrium between the pressure P(oil) of the oil and the pressure P(water) of the water.
The knowledge of various parameters and notably of the wettability of rocks is useful notably when enhanced recovery operations are to be carried out in a formation by draining the effluents it contains by injection of a pressurized fluid, and when preliminary tests have to be carried out to select the most appropriate fluid (water or gas) for displacing the effluents.
Different types of devices are used to carry out laboratory drainage and imbibition operations. Sample bars are generally placed in a cell. At its opposite ends, the cell comprises two ends communicating with means for displacing pressurized fluids through the sample tested. Measuring means are placed at different points along the bar in order to measure different parameters: pressures, saturations, electric resistivity, etc. The sample bar can be placed in an elastomer containment sheath compressed by injection of a pressurized fluid.
Different devices for measuring the physical parameters of porous solid samples are described for example in patent applications FR-2,603,040, EN. 93/09,481 or EN-94/10,783 filed by the claimant or in patents U.S. Pat. Nos. 4,868,751; 5,506,542 or 5,069,065.